1. Field of the Invention
This invention pertains, in general, to digital information storage systems, and in particular, to high capacity hard disk drives.
2. Description of the Related Art
Digital data may be stored on flexible or "floppy" disks or on hard or Winchester type disks by the magnetization of successive small areas on the magnetic surface of the disk, by means of a magnetic head or "slider", as the disk rotates. The density of digital storage on a hard disk memory system is on the order of 10 to 20 times the density achieved with floppy disk memory systems. In hard disk systems, the disks are normally formed of aluminum, and have a magnetizable coating on their upper and lower surfaces.
In order effectively to read and write information on the hard disks' magnetizable surfaces, a head positioner is typically provided within the drive wherein a plurality of rigid, interleaving head-positioning arms, each having one or more magnetic heads mounted on it, are assembled in a tandem, spaced relationship within an arm-positioning body containing an electromagnetic coil. The arm-positioning body is, in turn, rotatably mounted coaxially about a fixed shaft assembly, by means of steel bearing assemblies which attach between an inner surface of the arm-positioning body and outer surface of the rigid, fixed shaft. A separate but closely mounted permanent magnet structure provides a magnetic flux that operates in conjunction with the electromagnetic coil to achieve torque generation. A direct current applied to the coil permits the position of the arm-positioning body to be controlled by means of a feedback control loop within which a surface of one of the hard disks is dedicated to head-tracking and position control.
The alignment of the tracking head with the control disk within the servo loop is accordingly critical in terms of accuracy of overall head-position control. A misalignment within the mechanical chain of only a few microinches can cause reading or writing malfunction. This source of malfunction is especially prevalent when the subassembly comprising the arm-positioning body, along with the shaft and preloaded bearings installed, is assembled within the hard disk assembly. The mounting forces associated with the attachment of the shaft to the hard disk assembly may adversely affect bearing preload and can cause shaft misalignment and/or mechanical resonances which prevent the positioning servo mechanism from functioning properly.
It is therefore an object of the present invention to provide a hard disk magnetic head positioner which is more immune to the introduction of tracking errors introduced by the installation of the positioner within the overall drive assembly.